1. Field of the Invention
The present invention relates to an imaging apparatus including a reticle being capable of changing a diffusion coefficient, and a method for controlling the imaging apparatus.
2. Description of the Related Art
Conventionally, an optical finder of a single-lens reflex camera used as an imaging apparatus requires brightness of a finder image and easiness of holding of a focus peak. Herein, the easiness of holding of the focus peak means that the greater a blur effect of a defocus part such as a background is, the clearer a difference between a focus part and the defocus part is, and a focus is easily confirmed. Therefore, a diaphragm of a photograph lens is generally put into an open state during finder observation, and passes much light, to make the finder image bright. The diaphragm passes a light beam with an angle. Therefore, a depth of field which is a focusing range is narrowed, to easily blur the defocus part such as the background, and thereby the focus peak is easily held.
In the single-lens reflex camera, light from a photograph lens is reflected by a main mirror, to form a finder image on a reticle. A photographer observes the finder image through a pentaprism and an eyepiece lens. The reticle has unevenness. The reticle diffuses light, to change a direction of the light beam with an angle, and makes the light beam arrive at a photographer's pupil. Thereby, the photographer can see a blurred image. A diffusion characteristic of the reticle is represented by a diffusion coefficient (transmittance) as a ratio of transmitting light and diffusing light. The higher the diffusion coefficient of the reticle is, the more remarkable the blurred image is, and the finder image having a focus peak easily held is formed. On the other hand, the higher the diffusion coefficient is, the darker the finder image is. Conversely, the lower the diffusion coefficient is, the brighter the finder image is. However, the blurred image cannot be seen, and the finder image having a focus peak hard to hold is formed. It is difficult to satisfy both the brightness of the finder image and the easiness of holding of the focus peak with one reticle.
When the finder image is dark, a photographic subject and a composition are hard to see. When the focus peak is hard to hold, the photographer cannot confirm a focus in focusing by autofocus, and may take a photograph in which the targeted focus position is blurred.
Then, for example, Japanese Patent Application Laid-Open No. 6-258693 discusses following technique. A photographer optionally switches among a brightness priority mode, a focus priority mode, and a depth priority mode. The brightness priority mode gives priority to brightness of a finder using a reticle using liquid crystal and capable of changing a diffusion coefficient. The focus priority mode has the shallowest depth of field in the finder. The depth priority mode gives priority to expression of a depth of field in photographing.
However, when the photographer switches to the focus priority mode or the depth priority mode giving priority to the expression of the depth of field in photographing in the conventional technique discussed in Japanese Patent Application Laid-Open No. 6-258693, the entire finder image is dark, and the photographic subject is hard to see. Therefore, even if the blur effect of the defocus part such as the background is increased, the photographic subject image which is the focus part is dark and is hard to see, which disadvantageously makes it difficult to confirm the focus. The conventional technique requires provision of a focus frame projection unit based on an light emitting diode (LED), or a liquid crystal plate capable of displaying the focus frame independently of a reticle, in order to display a focus frame representing a focus range on a finder.